Erythrocyte aggregation: bridging by macromolecules and electrostatic repulsion by sialic acid

The Risk of Left Atrial Appendage Thrombus in Patients With Atrial Flutter Versus Atrial Fibrillation

Objective

Patients with atrial fibrillation (AF) are at increased risk of thromboembolic events originating mainly from left atrial appendage thrombus (LAAT). Patients with atrial flutter (AFL) are treated with anticoagulation based on the same criteria as patients with AF. However, whether patients with AFL have similar thromboembolic risk as AF is unclear. In the current study we aimed to estimate the prevalence of LAAT in patients with AFL undergoing trans-esophageal echocardiography (TEE).

Methods/results

We included 438 patients (404 with AF and 34 with AFL) scheduled for TEE to rule out LAAT before cardioversion (patients who reported no or inadequate anticoagulation before cardioversion). Demographic and echocardiographic data were compared between patients with and without LAAT. Despite a similar CHA2DS2-VASC score (3.8 ± 1.3 vs 3.4 ± 1.5 in the AF and AFL groups, respectively, P = .09), LAAT was documented in 12 (2.8%) in the AF group and in no patient in the AFL group (P < .0001).

Conclusion

Based on our results and previous studies, it seems reasonable to re-evaluate the need for oral anticoagulation in specific populations with AFL such as those with solitary AFL (without a history of AF episodes) undergoing successful ablation and in those with low CHA2DS2-VASC score.

Cytoplasmic anion/cation imbalances applied across the membrane capacitance may form a significant component of the resting membrane potential of red blood cells

Electrical aspects of cell function manifest in many ways. The most widely studied is the cell membrane potential, Vm, but others include the conductance and capacitance of the membrane, the conductance of the enclosed cytoplasm, as well as the charge at the cell surface (an electrical double layer) producing an extracellular electrical potential, the ζ-potential. Empirical relationships have been identified between many of these, but not the mechanisms that link them all. Here we examine relationships between Vm and the electrical conductivities of both the cytoplasm and extracellular media, using data from a suspensions of red blood cells. We have identified linear relationships between extracellular medium conductivity, cytoplasm conductivity and Vm. This is in contrast to the standard model of a resting membrane potential which describes a logarithmic relationship between Vm and the concentration of permeable ions in the extracellular medium. The model here suggests that Vm is partially electrostatic in origin, arising from a charge imbalance at an inner electrical double-layer, acting across the membrane and double-layer capacitances to produce a voltage. This model describes an origin for coupling between Vm and ζ, by which cells can alter their electrostatic relationship with their environment, with implications for modulation of membrane ion transport, adhesion of proteins such as antibodies and wider cell-cell interactions.

COVID-19, Cation Dysmetabolism, Sialic Acid, CD147, ACE2, Viroporins, Hepcidin and Ferroptosis: A Possible Unifying Hypothesis

Background: iron and calcium dysmetabolism, with hyperferritinemia, hypoferremia, hypocalcemia and anemia have been documented in the majority of COVID-19 patients at later/worse stages. Furthermore, complementary to ACE2, both sialic acid (SA) molecules and CD147 proved relevant host receptors for SARS-CoV-2 entry, which explains the viral attack to multiple types of cells, including erythrocytes, endothelium and neural tissue. Several authors advocated that cell ferroptosis may be the core and final cell degenerative mechanism.

Methods: a literature research was performed in several scientific search engines, such as PubMed Central, Cochrane Library, Chemical Abstract Service. More than 500 articles were retrieved until mid-December 2021, to highlight the available evidence about the investigated issues.

Results: based on COVID-19 literature data, we have highlighted a few pathophysiological mechanisms, associated with virus-based cation dysmetabolism, multi-organ attack, mitochondria degeneration and ferroptosis. Our suggested elucidated pathological sequence is: a) spike protein subunit S1 docking with sialylated membrane glycoproteins/receptors (ACE2, CD147), and S2 subunit fusion with the lipid layer; b) cell membrane morpho-functional changes due to the consequent electro-chemical variations and viroporin action, which induce an altered ion channel function and intracellular cation accumulation; c) additional intracellular iron concentration due to a deregulated hepcidin-ferroportin axis, with higher hepcidin levels. Viral invasion may also affect erythrocytes/erythroid precursors, endothelial cells and macrophages, through SA and CD147 receptors, with relative hemoglobin and iron/calcium dysmetabolism. AB0 blood group, hemochromatosis, or environmental elements may represent possible factors which affect individual susceptibility to COVID-19.    

Conclusions: our literature analysis confirms the combined role of SA molecules, ACE2, CD147, viroporins and hepcidin in determining the cation dysmetabolism and final ferroptosis in the cells infected by SARS-CoV-2. The altered ion channels and electrochemical gradients of the cell membrane have a pivotal role in the virus entry and cell dysmetabolism, with subsequent multi-organ immune-inflammatory degeneration and erythrocyte/hemoglobin alterations.

Hydrogen Gas Inhalation Prevents Erythrocyte Aggregation and Promotes Leukocyte Phagocytosis Together with Increases in Serum Antioxidant Activity

Hydrogen gas inhalation has not yet been elucidated to improve blood behaviors or antioxidant activity in blood. In the present study, the PEM (proton-exchange-membrane)-/platinum-plated electrode-equipped electrolyzer was examined as a hydrogen gas inhaler, which was estimated to supply 3% hydrogen as rapidly as post-operating 10–15 min, together with continuous 30 min retention of 20.8% oxygen being nearly equal to atmospheric oxygen contents. The 40 min inhalation of 3% hydrogen gas and thereafter 60 min rest were shown to enhance the antioxidant ability in human serum, as evaluated by ORAC (oxygen radical absorbing capacity)-based fluorometry, although scarcely enhanced for air dummy inhalation. Unexpectedly, antioxidant ability was 2.50-fold more enhanced for post-inhalational 0–60 min rest than during 40 min inhalation. Oxidative stress-suffering erythrocytes formed a rosary-chain-like aggregation composed of 3–6 cells, together with loss of a single hollow/biconcave-discoid structure in the cell central-part being necessary for erythrocyte passing through capillary vessels, both of which were prevented by 3% hydrogen gas inhalation. Hydrogen gas inhalation increased the intracellular foreign bodies, being distinguished from vacuole/cyst, in leucocytes, suggesting the hydrogen-activated leukocyte phagocytosis-associated events. Thus, 3%-hydrogen gas inhalation is suggested to potentially improve both the erythrocyte rheological/morphologic behaviors and the leucocyte phagocytosis-associated activity, concurrently with the enhanced antioxidant ability in blood.

Prevalence and predictors of left atrial appendage inactivity in patients of rheumatic mitral stenosis in sinus rhythm: An observational study

BACKGROUND

Systemic thromboembolism is a known complication of rheumatic mitral stenosis (RMS) in sinus rhythm (SR). Left atrial appendage (LAA), the commonest site of thrombus formation is usually hypocontractile (inactive) in such patients. We aimed to study the prevalence of LAA inactivity (LAAI) in severe RMS and assess its independent predictors.

METHODS

The study population consisted of 100 patients of severe RMS in SR. Transthoracic and transesophageal echocardiography were done to assess LAA contractile function. Patients with LAA-peak emptying velocity < 25 cm/seconds were defined as having LAAI.

RESULTS

The mean age of study subjects was 31.66±8.69 years and 56% were females. 73% patients had LAAI (Group A), while remaining 27% had normal LAA function (Group B). Mitral-valve area (MVA) and lateral annulus systolic velocity (Sa-wave) were significantly lower while mitral valve mean gradient (MVMG) and serum fibrinogen were significantly higher (all p-values < 0.001) in group A patients. On multivariate binary logistic regression analysis, MVMG (p < 0.001), Sa-wave (p = 0.02), and serum fibrinogen (p = 0.005) were independent predictors of LAAI. Optimal cut-off values of MVMG, Sa-wave and serum fibrinogen for predicting LAAI were 11.5 mm Hg, 6.8 cm/seconds and 300 mg/dl, respectively. Sixty-Seven (90.55%) patients in group A compared to 13(48.1%) in group B had LA/LAA smoke. LAAI was the only independent predictor of left atrium (LA)/LAA smoke with or without associated thrombus.

CONCLUSION

There is high prevalence of LAAI in patients of severe MS in SR. MVMG, Sa-wave, and serum fibrinogen levels are independent predictors of LAAI. LAAI is an independent predictor of LA/LAA smoke with or without associated thrombus.

Vm-related extracellular potentials observed in red blood cells

Even in nonexcitable cells, the membrane potential V_m is fundamental to cell function, with roles from ion channel regulation, development, to cancer metastasis. V_m arises from transmembrane ion concentration gradients; standard models assume homogeneous extracellular and intracellular ion concentrations, and that V_m only exists across the cell membrane and has no significance beyond it. Using red blood cells, we show that this is incorrect, or at least incomplete; V_m is detectable beyond the cell surface, and modulating V_m produces quantifiable and consistent changes in extracellular potential. Evidence strongly suggests this is due to capacitive coupling between V_m and the electrical double layer, rather than molecular transporters. We show that modulating V_m changes the extracellular ion composition, mimicking the behaviour if voltage-gated ion channels in non-excitable channels. We also observed V_m-synchronised circadian rhythms in extracellular potential, with significant implications for cell–cell interactions and cardiovascular disease.

Elevated serum sialic acids, a potent biomarker of alloxan-induced type 1 diabetes in dogs by ethanolic extract of Anogeissus leiocarpus

Objectives

This study investigated serum sialic acids for a predictive and diagnostic biomarker of diabetes mellitus (DM) in dogs and its prognostic value with ethanolic extract of Anogeissus leiocarpus.

Design

Four groups of 3 dogs were used; non-diabetic controls (ND), diabetic-untreated (DU), diabetic insulin-treated (DI) and diabetic extract-treated (DE). Free serum sialic acids (FSSA) and erythrocyte surface sialic acids (ESSA) were assayed in all groups, pre-and post-induction of hyperglycaemia and results were presented as means ± standard error of means (SEM) and subjected to ANOVA using Tukey's post-hoc tests with GraphPad Prism® statistical package.

Results

FSSA increased in DU and plateaued at third week (61.8 ± 0.41 μg/ml), (P < 0.002) with additional 38.2 μg/ml (62%) generated, coinciding with hyperglycaemia. FSSA of DI increased but declined to 22.3 ± 1.55 μg/ml. Extract of Anogeissus leiocarpus effectively modulated FSSA in DE as increased value declined to 21.4 ± 0.78 μg/ml. Pre-induction DU ESSA (8.27 ± 0.11 μg/ml) significantly (P < 0.002) decreased by third week (2.33 ± 1.49 μg/ml), coinciding with hyperglycaemia. Strong negative correlation coefficient (r = -0.92) occurred between DU's FSSA and ESSA and ND (P < 0.03). Sialic acid expression in dog's insulin dependent diabetes mellitus (IDDM) is 18% lower than normal. Extract of A. leiocarpus restored ESSA completely. ESSA cleaved in DU, 5.94 μg/ml (72%), could not account for the extra FSSA (32.26 μg/ml); liver and kidneys are contributors.

Conclusion

FSSA predicts canine DM.

Implication of d-dimer in rheumatic severe mitral stenosis – A tertiary centre study

Background

In rheumatic mitral stenosis (MS), left atrial (LA) thrombus and LA spontaneous echo contrast (LA SEC) reflect hypercoagulability. The study focuses on whether D-dimer levels predict the existence of LA thrombus and SEC in patients with severe MS.

Methods

95 consecutive patients with severe MS referred for transesophageal echocardiogram (TEE) between July 2011 and March 2012 to evaluate LA thrombus prior to balloon mitral valvotomy (BMV) were included in the study. D-Dimer levels in these patients were observed.

Results

Out of the 95 patients, 15 (15.8%) had LA thrombus and 52 patients had LA SEC (54.7%). Any correlation between D-Dimer levels and existence (or non-existence) of LA thrombus was not noticed from the receiver operating characteristics (ROC) curve with an area of .535. For patients with LA SEC, the D-Dimer levels were found to be considerably higher (776 ± 866 μg/L vs. 294 ± 331 μg/L, p = .001). An ideal cut-off level of 393 μg/L for diagnosing LA SEC was illustrated by the ROC curve with a sensitivity of 63.4%, specificity of 83.72%, positive predictive value of 82.5% and a negative predictive value of 65.45%.

Conclusions

D-dimer levels were not representative of the presence or absence of LA thrombus in patients with severe MS. Nonetheless, this study demonstrated the substantial link between D-Dimer level and LA SEC. If a D-Dimer level of 400 μg/L or higher is taken as positive, it has high specificity and positive predictive value for diagnosing LA SEC.

Surface-anchored framework for generating RhD-epitope stealth red blood cells

Rhesus D (RhD) is one of the most important immunogenic antigens on red blood cells (RBCs). However, the supply of RhD-negative blood frequently faces critical shortages in clinical practice, and the positive-to-negative transition of the RhD antigen remains a great challenge. Here, we developed an alternative approach for sheltering the epitopes on RhD-positive RBCs using a surface-anchored framework, which is flexible but can achieve an optimal shield effect with minimal physicochemical influence on the cell. The chemical framework completely obstructed the RhD antigens on the cell surface, and the assessments of both blood transfusion in a mouse model and immunostimulation with human RhD-positive RBCs in a rabbit model confirmed the RhD-epitope stealth characteristics of the engineered RBCs. This work provides an efficient methodology for improving the cell surface for universal blood transfusion and generally indicates the potential of rationally designed cell surface engineering for transfusion and transplantation medicine.

Left atrial spontaneous echo contrast: relationship with clinical and echocardiographic parameters

Spontaneous echo contrast (SEC) indicates blood stasis in cardiac chambers and major vessels, and is a known precursor of thrombus formation. Transesophageal echocardiography plays a pivotal role in detecting and grading SEC in the left atrial (LA) cavity. Assessing LA SEC can identify patients at increased risk for thromboembolic events. LA SEC also develops in patients who have sinus rhythm, especially in those with heart failure. Detection of LA SEC is not uncommon in subjects who have multiple cardiovascular comorbidities, although mechanisms behind this association are not fully understood. In patients with atrial fibrillation, the role of mitral regurgitation in counteracting LA SEC and subsequent thromboembolism is controversial. Moreover, alterations of blood coagulability and elevated levels of certain biological markers in the blood contribute to occurrence of LA SEC. This review describes the pathogenesis and assessment of SEC, in addition to the relationship between LA SEC and clinical, biological and echocardiographic parameters.

Erythrocyte Aggregation and Blood Viscosity is Similar in Homozygous Sickle Cell Disease Patients with and without Leg Ulcers

Background  There is no consensus regarding the role of red blood cell (RBC) aggregation in the pathogenesis of leg ulcers (LUs) in sickle cell disease (SCD). Objectives  We sought to evaluate whether the cross-sectional determination of RBC aggregation and hematological indices were associated with the presence of LU in homozygous SCD. Methods  Twenty-seven patients with LU and 23 with no history of ulceration were recruited into the study. A laser-assisted rotational red cell analyzer (LoRRca) was used in the determination of the aggregation index (AI), aggregation half-time ( t_1/2 ), and the RBC aggregate strength (AMP). Hematological indices were determined using a CELL-DYN Ruby analyzer. Whole blood viscosity (WBV) and plasma viscosity (PV) were measured using a Vilastic bioprofiler. The data were presented as means ± standard deviation or median, interquartile range. Two-sample t -test was used to test for associations between the AIs, WBV, and PV in patients with and without LU. Statistical significance was taken as p  < 0.05. All analyses were conducted using Stata/SE v . 12.1 (StataCorp, College Station, TX). Results  The AI was comparable in the group with and without ulcers (68.6, 16.7 versus 67.7, 16.9; p  = 0.74); t_1/2 (1.7, 1.3 versus 1.8, 1.3; p  = 0.71); AMP (18.8, 14.5 versus 19.1, 13.3; p  = 0.84), WBV (3.8, 1.2 versus 3.8, 0.7; p  = 0.77); and the PV (1.3, 0.08 versus 1.4, 0.1; p  = 0.31) and were also not statistically different between the groups of participants. Conclusion  RBC aggregation and aggregate strength are not associated with leg ulceration in SCD.

Comparison of the simple red blood cell adhesiveness/aggregation test with the laser-assisted optical rotational cell analyzer: Red blood cell aggregation in patients with coronary artery disease and a healthy control group

BACKGROUND

Red blood cell (RBC) aggregation influences blood flow properties, impacts blood microcirculation and consequently oxygen delivery. Different methods are established to determine RBC aggregation: under static conditions (i.e. the RBC adhesiveness/aggregation test (EAAT)) or under shear conditions (i.e. the laser-assisted optical rotational cell analyzer (LORCA)).

OBJECTIVE

Comparison of these two different methods in detecting the RBC aggregation of patients with coronary artery disease (CAD) and of healthy controls.

METHODS

RBC aggregation was quantified in peripheral venous blood of patients with CAD and healthy controls using EAAT and LORCA.

RESULTS

Both methods detected an increased RBC aggregation in patients with CAD compared to the healthy control group: the ratio of clot-free area to whole area (rCFA) detected with EAAT (15.65 vs. 11.30%), and aggregation index (66.33 vs. 53.90%), shear rate of disaggregation (SDA) (105.59 vs. 69.21 s-1), and upstroke/ttop (0.03 vs. 0.02 au/s) detected with LORCA device were increased, aggregation half time (detected with LORCA) was decreased (2.11 vs. 3.60 s). rCFA (EAAT) correlated with SDA (LORCA).

CONCLUSIONS

Both methods determine an increased RBC aggregation in patients with CAD. However, only one measurement parameter of the LORCA seems to reflect the same RBC aggregation properties as the EAAT.

Biochemical, Cellular, Physiological, and Pathological Consequences of Human Loss of N-Glycolylneuraminic Acid

About 2-3 million years ago, Alu-mediated deletion of a critical exon in the CMAH gene became fixed in the hominin lineage ancestral to humans, possibly through a stepwise process of selection by pathogen targeting of the CMAH product (the sialic acid Neu5Gc), followed by reproductive isolation through female anti-Neu5Gc antibodies. Loss of CMAH has occurred independently in some other lineages, but is functionally intact in Old World primates, including our closest relatives, the chimpanzee. Although the biophysical and biochemical ramifications of losing tens of millions of Neu5Gc hydroxy groups at most cell surfaces remains poorly understood, we do know that there are multiscale effects functionally relevant to both sides of the host-pathogen interface. Hominin CMAH loss might also contribute to understanding human evolution, at the time when our ancestors were starting to use stone tools, increasing their consumption of meat, and possibly hunting. Comparisons with chimpanzees within ethical and practical limitations have revealed some consequences of human CMAH loss, but more has been learned by using a mouse model with a human-like Cmah inactivation. For example, such mice can develop antibodies against Neu5Gc that could affect inflammatory processes like cancer progression in the face of Neu5Gc metabolic incorporation from red meats, display a hyper-reactive immune system, a human-like tendency for delayed wound healing, late-onset hearing loss, insulin resistance, susceptibility to muscular dystrophy pathologies, and increased sensitivity to multiple human-adapted pathogens involving sialic acids. Further studies in such mice could provide a model for other human-specific processes and pathologies involving sialic acid biology that have yet to be explored.

Significance of serum and urine neuraminidase activity and serum and urine level of sialic acid in diabetic nephropathy

BACKGROUND

Prospective studies have reported associations among various markers of inflammation and the incidence of diabetes, and it has been proposed that inflammation has a causal role in the development of diabetes. The objective of this study was to investigate the significance of serum and urine neuraminidase activity (NA) and serum and urine sialic acid (SA) level in patients with Diabetic nephropathy.

METHODS

In a prospective study, 190 diabetic patients with established diabetic nephropathy, 30 type 2 diabetes patients without any diabetic related nephropathy, and 36 non-diabetic patients with diagnosed nephropathy were enrolled. Two hundred and forty healthy individuals without diabetes or kidney disease were also enrolled as control group. Fasting venous blood samples and urine samples were collected and checked for serum and urine NA and SA level.

RESULTS

In the diabetic nephropathy group, the mean value of serum and urine NA was 64.6 ± 2.6 and 11.7 ± 1.2 mU/ml, respectively, and mean values of serum and urine SA were 93.2 ± 3.6 and 17.7 ± 1.4 mg/dl, respectively. Serum and urine NA and SA levels were significantly higher in patient with diabetic nephropathy when compared to the other groups (P < 0.001).

CONCLUSIONS

Our study suggests that there is a strong association between elevated serum and urine NA and serum and urine SA levels with the presence of diabetic nephropathy in type 2 diabetic patients. Further investigations are needed on the diagnostic and prognostic significance of these two inflammatory markers.

Chronic alcohol consumption augments loss of sialic acid residues and alters erythrocyte membrane charge in type II diabetic patients

In this study, the effects of alcohol consumption on erythrocyte membrane properties in type 2 diabetic patients were investigated. Therefore, we measured total and lipid-bound sialic acid (LSA) levels, sialidase activities, and erythrocyte membrane negative charge. Three groups, including control group (n = 20), alcohol-consuming diabetic patients group (n = 14), and diabetic patients without alcohol consumption group (n = 42), were created. Plasma total sialic acid (TSA) levels of the alcohol-consuming diabetic group were elevated as compared to the healthy control and diabetic group (p < 0.001 and p < 0.01, respectively). TSA levels of the diabetic group were significantly elevated as compared to the healthy control group (p > 0.001). Plasma LSA levels of the alcohol-consuming diabetic group were higher than that in the healthy control and diabetic group (p < 0.05 and p < 0.05, respectively). LSA levels of the diabetic group were found to be high as compared to the healthy control group (p < 0.05). Plasma sialidase activities of the alcohol-consuming diabetic group and diabetic group were significantly elevated as compared to the healthy control group (p < 0.05 and p < 0.05, respectively). Sialidase activities of the alcohol-consuming diabetic group were elevated as compared to the diabetic group, but this was not statistically significant (p > 0.05). Erythrocyte membrane negativity levels of the alcohol-consuming diabetic group and diabetic group were significantly decreased (p < 0.001 and p < 0.001, respectively) as compared to the healthy control group. Erythrocyte membrane negativity levels of the alcohol-consuming diabetic group were decreased as compared to the diabetic group, but this was not statistically significant (p > 0.05). In conclusion, our results indicate that chronic alcohol consumption may augment membrane alterations in type 2 diabetic patients.

Polyelectrolyte complexes based on (quaternized) poly[(2-dimethylamino)ethyl methacrylate]: behavior in contact with blood

Polyelectrolyte complexes (PECs) between (quaternized) poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) and (crosslinked) N-carboxyethylchitosan (CECh) or poly(2-acrylamido-2-methylpropane sodium sulfonate) (PAMPSNa) were prepared and characterized in terms of their stability, equilibrium water content, and surface morphology. The evaluation of the behavior of the studied PECs in contact with blood revealed that the (crosslinked) CECh/(quaternized) PDMAEMA complexes had lost the inherent PDMAEMA cytotoxicity but still preserved haemostatic activity. In contrast, the complex formation between (quaternized) PDMAEMA and PAMPSNa allowed the preparation of materials with improved blood compatibility.

Catheter-based impedance measurements in the right atrium for continuously monitoring hematocrit and estimating blood viscosity changes; an in vivo feasibility study in swine

Hematocrit is the most important determinant of whole blood viscosity and it affects thrombosis. As hematocrit can be measured accurately in vitro by using an electrical impedance technique, aim of the present study is to investigate the diagnostic potential of using this technique in vivo to continuously monitor hematocrit. Characteristics of a special catheter for in vivo measurement of electrical resistivity in blood in the right atrium are described. In five anesthetized swine hematocrit is monitored continuously with this catheter while different levels of hemoconcentration are induced. In addition, blood viscosity is increased by inducing 'acute phase' reaction the day before surgery, resulting in variable degree of elevated fibrinogen levels in the five swine. Good reproducibility of the resistivity measurements (S.D < 0.01) and excellent correlation between resistivity data in vivo and hematocrit levels in each swine are found (r2 = 0.95-0.99). Furthermore, stepwise regression analysis of data from all swine shows a highly significant contribution also of other important parameters of blood viscosity, such as fibrinogen, total protein and temperature (cumulative r2 = 0.97). Determining hematocrit continuously in vivo by electrical resistivity measurements with a catheter in the right atrium is feasible and these measurements correlate significantly also with other important parameters of blood viscosity.

Spontaneous echo contrast videodensity is flow-related and is dependent on the relative concentrations of fibrinogen and red blood cells

OBJECTIVES

The purposes of the present study were to: 1) determine whether fibrinogen (Fg) is the plasma protein responsible for spontaneous echo contrast (SEC), and 2) investigate modulators of SEC.

BACKGROUND

Spontaneous echo contrast has been linked to the development of thromboemboli. The blood products and their interaction responsible for SEC formation have not been fully elucidated.

METHODS

Blood echogenicity was examined with the use of quantitative videodensitometry over a controlled range of flow velocities in an in vitro model. Human blood samples were analyzed in a manner to methodically eliminate individual blood components from whole blood to determine which components are responsible for the formation of SEC.

RESULTS

The videodensity (VD) of whole blood was found to be flow-dependent, with higher VD at lower flow rates, and correlated with visually dense SEC. The following blood products produced faint VD values: washed red blood cells (wRBCs), platelet-depleted plasma, Fg, defibrinated plasma, wRBCs plus defibrinated plasma, and physiologic saline. The VD of wRBCs increased incrementally as increasing concentrations of Fg were added. At each hematocrit (Hct) range, as Fg concentration increased, the SEC became denser, and the VD level also increased until a plateau level was reached that was distinct for each Hct. The addition of sialic acid, which inhibits RBC-RBC aggregation, decreased the amount of SEC, even in the presence of Fg.

CONCLUSION

These results demonstrated that Fg-mediated RBC aggregation may be responsible for SEC generation. Furthermore, a unique stoichiometric relationship exists between Fg and RBC concentrations that is necessary for blood echogenicity.

Spontaneous echo contrast: where there's smoke there's fire

Left atrial (LA) spontaneous echo contrast (SEC), or "smoke," is a frequent finding on transesophageal echocardiography (TEE), but it is rarely detected with transthoracic echocardiography. LA SEC is characterized by dynamic smoke-like echoes within the LA cavity or appendage. Most patients with LA SEC have atrial arrhythmias, mitral stenosis, or a mitral valve prosthesis, and they have an enlarged LA, conditions that are associated with LA stasis. Conversely, mitral regurgitation is protective against LA SEC. LA SEC is present in almost all patients with LA thrombus and is associated with previous embolic events in many patient populations. In patients with nonvalvular atrial fibrillation, LA SEC predicts future embolism and death. LA SEC may therefore assist in selecting patients with atrial fibrillation or with mitral stenosis and sinus rhythm who benefit the most from anticoagulation. Hematological studies have shown that LA SEC is a marker of an hypercoagulable state. LA SEC is a manifestation of red cell aggregation, arising from an interaction between red cells and plasma proteins such as fibrinogen, at low shear rates. LA SEC does not require platelets. The detection of LA SEC on ultrasound arises from the increased amplitude of backscatter from red cell aggregates rather than single cells. Patients with LA SEC should be considered for anticoagulant therapy and may require correction of underlying cardiovascular abnormalities. Future directions in LA SEC include further assessment of integrated backscatter for quantification, assessment of its prognostic role in clinically low-risk patients with nonvalvular AF, and novel pharmacological treatment.

Alteration of red cell aggregability and shape during blood storage

BACKGROUND

Storage of blood units (for 35-42 days, depending on the preservative solution) has been reported to induce changes (e.g., reduction of sialic acid level) in red cells that are expected to alter their aggregability.

STUDY DESIGN AND METHODS

The aggregability of stored red cells was monitored in their autologous plasma and compared to that obtained with washed cells in dextran-containing buffer throughout the storage period. Red cell aggregability was determined by using a computerized image analyzer of cell flow properties.

RESULTS

Blood storage induced changes in red cells that are associated with continuous increase of their aggregability. At the same time, blood storage was associated with a reduction in the level of plasma fibrinogen, the major aggregating agent in plasma. Accordingly, the increased red cell aggregability was observed in red cells stored in dextran-containing buffer, but not in red cells stored in autologous plasma.

CONCLUSION

Because blood transfusion is routinely given to patients with normal or high fibrinogen level, the transfusion of stored red cells has the potential to induce increased aggregation in vivo, depending on the storage period. This should be taken into account when blood transfusion is considered, particularly for patients with microcirculatory disorders.

Expression of cell adhesion molecules and the appearance of adherent leukocytes on the left atrial endothelium with atrial fibrillation: rabbit experimental model

To assess the expression of cell adhesion molecules and the appearance of leukocytes adhering to the left atrial endothelium with atrial fibrillation (AF), 10 Japanese white rabbits were anesthetized and 3 pacing leads were placed in the right atrium. For the AF model, the right atrium was stimulated by electrical pacing (the stimulation frequency of each lead being adjusted to different intervals) for 8h while the control model was subjected to a sham operation without atrial stimulation. The left atrial appendage was excised from the heart and examined immunohistochemically. P-selectin staining of the endothelium in both models was linear and regional, and intracellular adhesion molecule-1 (ICAM-1) in the AF model was confined to leukocytes and endothelial cells with adherent leukocytes. The expression of P-selectin (p<0.05) and the appearance of positively ICAM-1 stained adherent leukocytes (p<0.05) were significantly greater in the AF model than in the control model. In conclusion, AF could regulate the expression of at least 2 critical adhesion molecules, P-selectin and ICAM-1, and the appearance of adherent leukocytes; suggesting that these molecules may play an important role in left atrial thrombus formation with AF. Although anticoagulant therapy has generally been carried out with warfarin in AF patients, neutralizing antibodies to cell adhesion molecules should be tried to prevent thromboembolic complications.

Fine structural and functional consequences of deglycosylation of the platelet adhesion receptor GPIb-IX (CD 42b)

To investigate the role of the glycosylation of the platelet receptor glycoprotein Ib (GPIb, CD 42b), platelets and purified GPIb were deglycosylated by neuraminidase, O- and N-glycosidases. N-deglycosylation and neuraminic-acid cleavage had little effect on ristocetin and botrocetin-induced platelet agglutination. However, O-deglycosylation reduced the response by approximately 50%, and total deglycosylation (the combination of all three glycosidases) fully abolished the response to ristocetin. Interestingly, binding of von Willebrand Factor (vWF) to purified GPIb in the presence of ristocetin and botrocetin in a standardized microtiter plate assay was not altered by partial or even by total deglycosylation. Electron microscopy indicated that the normally stretched approximately 50 nm long molecule was approximately 32 nm after N-deglycosylation, approximately 20 nm after O-deglycosylation, and reduced in a approximately 15 nm long collapse by total deglycosylation. These results suggest that deglycosylation has major structural impacts on GPIb, strongly impairing platelet-vWF interactions; however, vWF binding to isolated GPIb remains unaffected.

Sialic acid, transketolase and Na+, K+, ATPase in patients with rheumatoid arthritis

We studied transketolase activity of red blood cell hemolysates, and Na+, K+, ATPase activity and sialic acid concentration in red blood cell membranes from 52 patients with rheumatoid arthritis and 24 control subjects. Decreased red blood cell membrane Na+, K+, ATPase activity and sialic acid concentration and decreased transketolase in red blood cell hemolysates were observed in rheumatoid arthritis patients compared with control subjects (p < 0.001). Erythrocyte sedimentation rate and C-reactive protein values were increased in rheumatoid arthritis patients compared with control subjects (p < 0.0001). Significant correlations between sialic acid and Na+, K+, ATPase (r = 0.65, p < 0.001) and between sialic acid and transketolase (r = 0.58, p < 0.001) were observed. Erythrocyte sedimentation rate and C-reactive protein levels did not correlate with Na+, K+, ATPase activity or with sialic acid or transketolase in rheumatoid arthritis patients. These data show that decreases in Na+, K+, ATPase, and transketolase activities and sialic acid concentration are present in rheumatoid arthritis patients, and that the decrease in Na+, K+, ATPase and transketolase activities in rheumatoid arthritis might be due to decreased sialic acid.

Sialic acid, diabetes, and aging: a study on the erythrocyte membrane

Sialic acid (SA) content and Na+/K+-ATPase activity of red blood cell (RBC) membranes were studied in 26 normoalbuminuric patients with insulin-dependent diabetes mellitus (IDDM), 25 normoalbuminuric patients with non-insulin-dependent diabetes mellitus (NIDDM), and 40 healthy nondiabetic subjects with a negative family history for diabetes. A decrease in RBC membrane SA content and Na+/K+-ATPase activity was observed in older control subjects compared with younger controls. A significant correlation between age, Na+/K+-ATPase activity, and SA content was also found. No difference was observed in RBC membrane SA content between IDDM and NIDDM subjects, but Na+/K+-ATPase activity was significantly lower in IDDM patients. SA content was increased in NIDDM subjects compared with healthy subjects of similar age, whereas Na+/K+-ATPase activity was significantly lower in both IDDM and NIDDM subjects compared with controls. In NIDDM, Na+/K+-ATPase activity was significantly correlated with age, whereas both Na+/K+-ATPase activity and SA content were significantly correlated in IDDM and NIDDM patients. Hemoglobin A1c, (HbA1c) levels did not show any significant correlation either with Na+/K+-ATPase or with SA content in diabetic patients. The modified SA content and Na+/K+-ATPase activity in elderly subjects described in the present study indicate a similar behavior of the erythrocyte membrane during both RBC senescence and aging of subjects.

Do physiological concentrations of IgG induce a direct aggregation of red blood cells: comparison with fibrinogen

Under physiological conditions, red blood cells (RBCs) form aggregates that allow blood flow in all the circulatory system. RBC aggregation is the result of local flow shear stress, erythrocyte properties and macromolecular interactions between adjacent cells. Plasma proteins like fibrinogen or IgG are considered to promote RBC aggregation by a mechanism that remains to be explained. In the present study, we have examined the precise role of IgG on RBC fast-phase aggregation, in comparison with that of fibrinogen. Under our experimental conditions, we observed no fast-phase aggregating effect for IgG, at either physiological or supraphysiological concentrations, while fibrinogen induces strong aggregation of RBC. We also suspect the other plasma proteins to play a role in the RBC aggregating process.

Enhancement of erythrocyte sedimentation rate by polymerized hemoglobin

Development of hemoglobin-based blood substitutes requires the scrutiny of blood rheological parameters that could be influenced by this class of molecules. Accordingly, we have examined the effects of glutaraldehyde-polymerized human hemoglobin on the erythrocyte sedimentation rate (ESR). For this purpose, human hemoglobin (Hb) was polymerized by glutaraldehyde, and its progress was monitored by gel permeation. ESR was measured by addition of hemoglobin or polymerized Hb (Poly-Hb) to citrated rat whole blood. The results indicate that, whereas Hb exerted minimal perturbation of ESR, Poly-Hb obtained under some polymerization conditions induced an over fifty-fold elevation of ESR. When polymerized Hb was fractionated by size, and different fractions were tested for their effects on ESR, a sharp dependence of ESR enhancement on molecular size of polymerized Hb was found. These observations suggest that ESR enhancement is mediated by macromolecular bridging formed by Poly-Hb of an adequate length between the surfaces of two stacking erythrocytes.

Evidence that cell surface charge reduction modifes capillary red cell velocity-flux relationships in hamster cremaster muscle

1. From capillary red cell velocity (V)-flux (F) relationships of hamster cremaster muscle a yield velocity (VF = 0) can be derived at which red cell flux is zero. Red cell velocity becomes intermittent and/or red blood cells come to a complete standstill for velocities close to this yield velocity, and, at the same time, capillary tube haematocrit becomes very low. 2. We have tested whether the net negative charge of red blood cells (RBCs) contributes to the magnitude of VF = 0. Velocity-flux relationships were measured for normal cells, normal cells labelled with the fluorescent dye calcein (LRBCs), and red cells treated with hexadimethrine to mask negative charge and labelled with calcein as well (HDM-LRBCs). Measurements were done in a hamster cremaster muscle preparation applying video in vivo microscopy. 3. Hexadimethrine treatment reduced the net negative surface charge of red cells to 20% of control as estimated from transmission electron microscopy using a ferritin tagging technique. The values of VF = 0 found for normal red cells and HDM-LRBCs were 86 +/- 15 and 31 +/- 17 microns s-1, +/- S.E.M., n = 12, respectively, which were significantly different (P < 0.05). For normal cells and cells labelled with calcein only, VF = 0 values were 63 +/- 14 and 65 +/- 13 microns s-1, n = 8, respectively, which were not significantly different. The effect of HDM treatment did not alter filterability of the red cells as estimated from transit times through 5 microns pores. 4. The present findings demonstrate that the net negative charge of RBCs contributes significantly to the yield velocity for red blood cells entering capillaries and flowing through them. HDM treatment reduced the net negative charge of red blood cells and may have caused cells to enter capillaries more easily owing to reduced electrostatic repulsion at the capillary entrance. In addition, HDM treatment may have lowered intracapillary flow resistance by a reduction in electrostatic repulsive forces between red blood cells and negatively charged (macromolecules on) capillary endothelial cells at sites of irregular capillary cross-sectional shape, without significantly affecting the lubricating properties of the capillary endothelial glycocalyx and/or associated plasma macromolecules.

Interactions of macromolecules with the mammalian cell surface

The characterisation of fluoresceinphosphatidylethanolamine (FPE) as a real-time indicator of the electrostatic nature of the cell membrane surface is described. The conditions appropriate for the labelling of cell membranes and the implementation of FPE as a tool to monitor the interactions of various proteins and peptides with membranes are outlined. Some complications attributed to the erythrocyte glycocalyx are examined. In addition it is shown using neuraminidase as an example, that some types of enzyme-catalysed reactions on the cell surface may be monitored in real time. It is also shown that information concerning the binding of several proteins such as serum albumin and monoclonal antibodies are accessible with this technique. The albumin in particular is shown to exhibit a saturation of binding, the analysis of which indicates that the dissociation constant for erythrocytes was determined to be 8 microM and for lymphocytes to be almost 3 microM. On the basis of this comparison together with artificial membranes, the membrane protein components of the lymphocyte surface are implicated in the binding of albumin or the erythrocyte membrane proteins reduce the affinity of the cell surface for albumin.

The role of echocardiography in the evaluation of cardiac source of embolism: left atrial spontaneous echo contrast

Left atrial (LA) spontaneous echo contrast, also known as "smoke," is a frequent transesophageal echocardiographic finding characterized by swirling, smokelike echoes in the LA cavity or appendage. LA smoke is associated with conditions favoring stasis of LA blood, including atrial fibrillation, mitral stenosis, the absence of mitral regurgitation, and LA enlargement. LA spontaneous echo contrast is a marker of previous embolic events in patients with atrial fibrillation, mitral stenosis, or mitral valve replacement. Most LA thrombi are accompanied by smoke. Recent studies show that LA spontaneous echo contrast is also associated with increased fibrinogen, hematocrit, and blood viscosity, indicating a relatively hypercoagulable state in addition to stasis. These findings suggest that LA spontaneous echo contrast is a manifestation of erythrocyte aggregation, and that hematologic factors may contribute to the association between spontaneous echo contrast and thromboembolism.

Hematologic correlates of left atrial spontaneous echo contrast and thromboembolism in nonvalvular atrial fibrillation

OBJECTIVES

This study examined the relation between left atrial spontaneous echo contrast, hematologic variables and thrombo-embolism in patients with nonvalvular atrial fibrillation.

BACKGROUND

Left atrial spontaneous echo contrast is associated with left atrial stasis and thromboembolism in patients with nonvalvular atrial fibrillation. However, its hematologic determinants in patients with nonvalvular atrial fibrillation are unknown.

METHODS

Clinical, hematologic and echocardiographic variables were prospectively measured in 135 consecutive patients with nonvalvular atrial fibrillation undergoing transesophageal echocardiography.

RESULTS

Patients with left atrial spontaneous echo contrast (n = 74, 55%) had an increased fibrinogen concentration (p = 0.029), platelet count (p = 0.045), hematocrit (p = NS) and left atrial dimension (p = 0.005). Multivariate analysis showed that left atrial spontaneous echo contrast was independently related to hematocrit (odds ratio = 2.24, p = 0.002), fibrinogen concentration (odds ratio = 2.08, p = 0.008) and left atrial dimension (odds ratio = 1.90, p = 0.004) but not platelet count. It was also associated with left atrial thrombus (n = 15, p = 0.001) and with recent embolism (n = 40, p < 0.001). In 40 clinically stable outpatients without previous embolism, left atrial spontaneous echo contrast was significantly related to hematocrit (p = 0.005), fibrinogen concentration (p = 0.035) and left atrial dimension (p = 0.029) but not to coagulation factor VII, D-dimer, erythrocyte sedimentation rate, platelet count, plasma beta-thromboglobulin, plasma glycocalicin or glycocalicin index.

CONCLUSIONS

Left atrial spontaneous echo contrast in patients with nonvalvular atrial fibrillation is independently related to hematocrit, fibrinogen concentration and left atrial dimension, indicating a relatively hypercoagulable state in addition to stasis. These findings support the hypothesis that left atrial spontaneous echo contrast is due to erythrocyte aggregation. Hematologic factors may contribute to its association with thromboembolism.